Hey guys, so I've been playing guitar now for about a year and a half, I've come a long way since I first started, making major strides in advanced techniques such as sweep picking and economy picking, and am able to play accurately and clean at speed. Having started guitar a year and a half ago I've been playing roughly 3-6 hours a day, and I have noticed a huge increase in strength and dexterity of my left hand, however I have come across a problem;

The problem I'm having is not that I can't move my fingers at this speed, but I am having trouble isolating my 3rd finger to hit on the 7th fret. When I try to play it fast it ends up being something like 8-6-5-5, picking it the correct amount of times (4 times) but completely missing the 7th fret. I don't seem to have control over my 3rd finger enough to hit the 7th fret when picking at high speeds. I've tried the good ol "Try it slow, then build up speed" but it doesn't seem to be working, because it feels like the problem is not my speed but rather the lack of control of my 3rd finger. I can hit a run of 5-6-7-8 from low E to high E at good speeds, accurate and clean, without any problems, it just seems to be when I need to pull off my pinky from the 8th fret and fret the 7th fret with my ring that I get this lack of control problem.

If anyone can give any exercises or experiences with this problem then please share in this thread as it has really boggled me and at some times frustrated me!

Firstly you must understand: there is no such skill as speed, there is only control.

If you can't control your fingers well enough at the speed you want to play at then you are unable to play at that speed, pure and simple. You need to sped more time playing at lower tempos until you have the kind of control required.

Don't build up speed, just practice.

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Sounds like you have to slow down and practice basics alot more. You may feel like your covering alot of ground by tackling the more difficult and fun techniques, but as a result you may develop really bad habits that won't allow you to play what would otherwise be a very simple lick.

EDIT: My advice would be to treat this riff as an exercise and practice it regularly.

place your left hand flat on a table and try lifting up your fingers, one by one, one at a time. you'll find that you can't lift your ring finger anywhere near as high or as easily as the others. this is thanks to how the muscles are connected in your hand, but generally it just shows that when it comes to doing descending licks it'll be the parts that use your little finger then your ring that'll be the hardest, thanks to this and the fact that little fingers are just rubbish.
but yes, you can obviously play this pattern at a very slow speed, and you can't play it at a very high speed, so there's somewhere in the middle that is your breaking point. find that and go a few bpm slower.